1. Field of the Invention
The present invention relates generally to structures and materials used in the formation of orthopedic casts. The present invention relates more specifically to a layered, open cell, fabric material impregnated with a curable polymer or prepolymer resin that may be shaped and formed prior to curing into a rigid cast.
2. Description of the Related Art
Orthopedic casting materials have evolved over time from the earlier plaster of Paris and cotton gauze based casts to the more recent synthetic orthopedic casting tapes. Plaster of Paris based casts suffered from many difficulties that included being generally air impermeable, being subject to deterioration in contact with water, and being very heavy and bulky. The basic structure of the more recent synthetic casts involves a fabric sheet or tape, usually of fiberglass, that is impregnated with a liquid resin that cures and hardens in air over a short period of time. Alternate materials include thermoplastic resins that are formable at a temperature higher than room temperature but not so high as to be uncomfortable to the patient or the individual putting the cast material in place. In either case the result is a strong, relatively lightweight cast that, after curing, is not subject to deterioration in contact with water.
Fiberglass/Polymer Resin based cast materials typically come in two structural forms. The basic form involves a roll of tape anywhere from one to five inches wide that is applied by wrapping the tape around the limb to be cast. A second general structural form involves a pre-cut sheet of the material sized and shaped to fit around a specific appendage such as a wrist and forearm or an ankle and foot. The latter configuration is typically easier to apply but less conformable to the variety of sizes and shapes of limbs. The former structure (tape) is more versatile but is generally more difficult to apply.
The optimal characteristics of casting materials can be countervailing or conflicting in many cases. Obviously the material must result in a cast of sufficient strength to protect the healing limb. There is also however the desire for the cast to be lightweight and less bulky. As indicated above, it is desirable for the casting material to be readily formable prior to curing so as to more closely support and guard the limb. The resin-based materials should not overly adhere to the patient""s skin or to the hands or gloves of the individual putting the cast in place. It is also important for the material to be readily removable when the limb has healed. Finally the finished cast should be resistant to deterioration in contact with water (and perspiration and the like) but should also be breathable. Significant skin maceration and patient discomfort can occur as a consequence of deficiencies in breathability. It has been most difficult to provide a material that is sufficiently strong and at the same time is lightweight and breathable.
There have been many efforts to improve upon both the structures and substance of the basic fiberglass/polymer resin casting material. Some of these efforts have focused on the type of resin used and the benefits of specific compositions. Other efforts have focused on the structure of the foundation fabric and the benefits of specific weaves and fiber geometry. Various patents reflecting some of these efforts include the following:
U.S. Pat. No. 5,584,800 issued to Scholz et al. on Dec. 17, 1996 entitled METHOD OF ENCLOSING A BODY MEMBER USING AN APERTURED EXTRUDED SHEET describes an extruded casting sheet made of a low temperature thermoplastic polymer that is soft and pliable above about 90xc2x0 C. The material described may also include filler associated with the resin to improve its handling characteristics.
U.S. Pat. No. 5,461,885 issued to Yokoyama et al. on Oct. 31, 1995 entitled SUBSTRATE FOR RETAINING A HARDENABLE COMPOSITION describes specific fabric knit structures that are impregnatable with hardenable resin by capillary action. The material described is directed to combining strength and good air permeability.
U.S. Pat. No. 4,856,502 issued to Ersfeld et al. on Aug. 15, 1989 entitled CURABLE RESIN COATED SHEETS HAVING REDUCED TACK describes a non-woven fiber material that leaves small apertures or openings in the fabric sheets. The focus of the patent, however, is on the incorporation of additive or bound lubricants in the resin to facilitate the application of the cast without undesirable adhesion.
U.S. Pat. No. 4,841,958 issued to Ersfeld et al. on Jun. 27, 1989 entitled NONWOVEN ORTHOPEDIC CASTING MATERIALS WITH APERTURES describes yet another foundation made of a non-woven stretchable fabric impregnated with a curable prepolymer resin. The fabric is made of fiber bundles that receive and retain the resin and which form small openings between the bundles that remain open after curing.
U.S. Pat. No. 4,683,877 issued to Ersfeld et al. on Aug. 4, 1987 entitled ORTHOPEDIC CASTING ARTICLE AND METHOD describes a pre-cut, shaped xe2x80x9cblankxe2x80x9d of layered cast material that includes an extensible woven fabric and a layer of extensible foam. The pre-cut casting blank is sized and shaped to fit a particular limb and is initially held in place (prior to curing) by a number of clips that secure an edge of the material to the surface of the material upon wrapping around the limb.
U.S. Pat. No. 3,998,219 issued to Mercer et al. on Dec. 21, 1976 entitled ORTHOPEDIC SPLINT AND METHOD FOR FORMING SAME describes a multi-layered cast material comprising a central cellular core and inner and outer layers that sandwich the core and which when cured are rigid and supportive. Optional layers of foam material may be placed between the core and the inner and outer layers to provide better interlock between the layers (to reduce shifting between the layers).
Although a number of the materials described in the above references have as their stated goal a certain amount of air permeability, such properties remain less than optimal given the small size (on the order of 1 mm or less) of the apertures formed. In addition, none of the above materials accomplish much in the way of significantly reducing the size and weight of the finished cast. In general it is the resin (in a cured state) that provides the structural strength to the cast it is also the resin that contributes the most to the weight of the cast. Because of this problem, prior efforts have greatly limited the size of the openings or apertures in the fabric in order to maintain a sufficient amount of hardenable resin dispersed throughout the cast tape or sheet.
It is therefore an object of the present invention to provide a material for use constructing orthopedic casts of the fiberglass and hardenable resin type that significantly reduces the size and weight of the resultant cast structure.
It is another object of the present invention to provide a material for use in forming orthopedic casts that incorporates apertures of a size, number and arrangement that significantly increases the amount of air flow through the cast in comparison to existing open mesh cast materials.
It is a further object of the present invention to provide an open mesh cast material that incorporates foundational fabric material compositions and additive hardenable resin compositions that are known and utilized in the art.
It is a further object of the present invention to provide an open mesh cast material that provides sufficient rigidity without increased weight and size. It is a related object to address the foregoing through cast materials having optimal geometries.
It is a further object of the present invention to provide a material for use in forming orthopedic casts that may be precut and partially preformed to accommodate standard limb sizes and shapes.
It is a further object of the present invention to provide a material for use in forming orthopedic casts that while providing a rigid protective enclosure for the injured limb, may still be easily removed through the use of scissors or cast saws.
It is a further object of the present invention to provide a material for use in forming orthopedic casts that incorporates a continuous hexagonal conduit array within which are positioned microbeads or the like and which when subjected to a negative pressure differential becomes rigid.
Other objects and advantages will be apparent to those of ordinary skill in the art from the following disclosure.
In fulfillment of these and other objectives the present invention provides a fiberglass and hardenable resin based orthopedic casting material made from layers of resin impregnated fiberglass fibers that are shaped, cut, or otherwise formed into a skeletal hexagonal cellular mesh array. The material forms a generally sheet-like element having an array of apertures there through to permit the flow of air through the cast as well as the visual and physical monitoring of the condition of the patient""s injured limb. The size of the hexagonal apertures in the material may vary according to the specific application of the cast but is generally large in comparison to the cross sectional size of the fiberglass sections that define the sides of the hexagonal apertures. Reinforcing strand components, such as stainless steel and Kevlar(copyright) fibers may be incorporated into the casting material. Optionally the mesh may incorporate a lining that prevents the resin from adhering to the skin. The sheet-like material may be cut and trimmed both prior to application in its pliable state and subsequent to application in its rigid state. The apertures in the material serve to receive the fingers or toes of the individual receiving the cast in a manner that facilitates the application of the material. Furthermore, the apertures serve the primary purpose of allowing nearly complete air flow through the cast to permit the rapid drying of the cast and the skin after wetting occurs. The skeletal structure of the material greatly reduces the size and weight of the cast without unduly sacrificing strength and protection.